When the indoor unit of an air conditioner is driven in a cooling mode, the vapor in the air will condensate and adhere to a heat exchanger, and drops to a drainage pan mounted underneath. A drainage pump is equipped for draining the drainage water gathered in the drainage pan. There are many varieties of such drainage pumps proposed in the prior art. For example, a prior art drainage pump comprises a housing having a suction inlet at the lower portion, an opening at the upper portion, and a discharging outlet on the side, and a vane mounted rotatively inside the housing. The vane rotates by a motor fixed via a cover to the upper portion of the opening of the housing. The rotation shaft of the motor extends through the cover rotatively and is connected to the shaft of the vane. The cover is equipped with a through hole for connecting air and the housing. When the motor is driven and the vane rotates, the drainage water gathered inside the drainage pan will be sucked in from the lower end of the vane of the suction inlet, is pumped along the inner surface of the housing, and discharged from the discharging outlet of the casing.
The operation of a drainage pump of the prior art of the above type disclosed in Japanese Patent Laid-Open No. H8-144996 is shown in FIGS. 3A and 3B. FIG. 3A shows the upper view of the interior of the drainage pump, and FIG. 3B shows the front view of the interior of the drainage pump. FIG. 3A depicts the bubbles.
A pump body 10 of a drainage pump 1A comprises a pump chamber 12, a suction inlet 15 and a discharging outlet 17. A rotation vane 100 equipped inside the body 10 is connected to a motor (not shown) mounted on the upper portion of the pump body 10 and comprises a shaft 110, four large vanes 120 and a cutwater board 34, wherein a gap 32 is formed between the shaft 110 and the cover 30 of the body. Underneath the large vane 120 is a small vane 130 for raising the drainage water sucked in from the suction inlet. A disc 150 is connected to the lower peripheral of the large vane 120. The disc 150 includes a hollow portion 155 for keeping back and dividing a portion of the drainage water rising from the suction inlet. As a result, the amount of water contacting the large vane 120 at the upper portion of the disc 150 decreases, and the load that the rotation vane receives will reduce. At the same time, the collision of the bubble and the vane will decrease, reducing noise and vibration.
In a prior art drainage pump as is described above, when the stage of the water is low or the lift is low at the suction inlet 15, the liquid-vapor boundary surface formed on the inner side of the drainage stream will be divided by the disc 150 as is shown by W.sub.2, and a portion of the drainage water will be kept back. However, when the stage of the water is high or the lift is high, the liquid-vapor boundary surface will form a connected curve surface as is shown by W.sub.1, and the drainage water will not be divided at the liquid-vapor boundary surface. Therefore, the drainage water contacting the large vane 120 will increase, and the collision of the bubble and the vane will increase, causing noise. This may prevent the decrease of noise necessary in the indoor unit of air conditioners.
Therefore, the present invention aims at providing a drainage pump with decreased noise even when the stage of the water is high or the lift is high.